1. Field of the Invention
The present invention relates to a switching converter circuit applicable to various types of electronic units. More particularly, the present invention relates to an interleaved switching converter circuit in which a plurality of switching converters, connected in parallel to each other, are alternately turned ON/OFF, and to a method for controlling the switching converters.
2. Description of the Related Art
Various types of interleaved switching converter circuits are described, for example, in Japanese Laid-Open Publications Nos. 61-288780, 1-231661 and 1-270769, U.S. Pat. No. 5,508,903 and the like. In a prior art switching converter circuit, assuming that the switching converter circuit includes a number N (where N is an integer equal to or larger than 2) of switching converters, the switching converters are alternately turned ON/OFF with a phase difference of 360/N degrees. For example, if an interleaved switching converter circuit includes two switching converters (i.e., N=2), the two switching converters included therein are alternately turned ON/OFF with a phase difference of 180 degrees. Under such a configuration, the amplitude of a ripple generated in input/output current can be reduced and the frequency of the ripple can be increased. In addition, since a load applied onto input/output filters can be reduced, the filters can be downsized.
In such a conventional interleaved switching converter circuit, since the respective switching converters are turned ON/OFF with an appropriate phase difference, the switching frequency is fixed. Thus, it has been impossible to form an interleaved switching converter circuit by combining such switching converters as ringing choke converters having a switching frequency which is variable depending upon input/output conditions.